Catalytic agent for use in producing ammonia.



' monia could be obtained in any case, unless' UNITED STATES PATENT OFFICE.

CARL BOSCH, m'rascn, AND HANS WOLF, OI LUDWIQ'SHAIEN ON-THE-RHINE, AND GEOBG STERN, OF KANNHEIH, GEBIANY, ASSIGNOBS TO BAIDISCHE ANILIN & SODA FABBIK, OI LUDWIGSHAFEN-ON-THE-BHINE, GERMANY, A CORPORATION.

CATALYTIC AGNN'I FOR USE IN PRODUCING AMMONIA.

Io Drawing.

To all whom it may concern:

Be it known that we, CARL Boson, ALWIN Mrr'rasen, Hans Wow, and Gnoao STERN, doctors of philosophy and chemists, subjects the first and fourth of the King of Prussia, the second of the Kin of Saxony, and the third of the King of avaria, residin -the first three at Ludwigshafen-omthe-R ine, Germany, and the fourth at Mannheim, Germany, have invented new and useful Improvements in Catalytic A nts for Use in Producing Ammonia, of w ich the following is aspecification.

Our invention relatesto catalytic a nts suitable for use in the manufacture 0 ammonia by synthesis from its elements.

It has long been known that small quantities of ammonia can be produced synthetically from its elements by passin them over a catalytic agent. Thus Flee (cf. Bolleys .Handbuch der chemisohon Technolo'gze, '1862, II, pp. 2, 48) stated that ammonia could be obtained by passing a mixture of nitrogen, carbon monoxid and steam over hot lime. Ramsay and Young (J ourmoi of the Chemical Society, 1884, vol. p. 93) stated that on passing a mixture of dry nitro on and hydrogen over iron filings containe in a red hot glass tube they were unable to observe that any ammonia had been formed, while if moist gases were used ammonia, but only a trace, was formed. Perman, in the Proceedings of the Royal Society (vol. 76, p. 167, etc.), describes experiments made by passing nitrogen and hydrogen over iron and stated that no amthe iron was at a bright red heat, and the largest yield heobtained consisted of onefifth of a milligram from 250 0. cm. of mixed gases. Haber and van Oordt (Zeitsohrift fair anorganische Uhemie, 44, 341) and Haber and Le Rossignol (Berio te,'40,

' p. 2146) experimented on the production of ammonia from nitrogen and hydro en by passing them over iron-asbestos, an iron, nickel, chromium, and manganese, but the results obtained by them and also by Nernst and Jost (Zeitsclmift fair anorganisohe Uhemz'e, 57, p. 414) led to the conclusion that a practical manufacture of ammonia synthetically from its elements by passing them over such a catal) tic agent as the known forms of iron or the like was out of Specification of Letters Patent.

J Application Med December 24, 1810. Serial No. 599,101.

Patented Aug. 3, 1915.

the manufacture of ammonia, and moreover the small yield which may be obtained does not remain constant, but usually diminishes more or less rapidly.

We have now discovered a new form of iron by the use of which as a catalyst the manufacture of ammonia is rendered possible. For instance, with our new iron we obtain from a mixture of nitrogen and hydro en, in Epractical working, say as deseri ed in xample 16 a mixture of gases oontainin upward of ei ht per cent. by volume 0 ammonia, and t is yield remains practically constant, for instance when the iron has been in use for at least several weeks.

Our invention, however, "is not restricted to such iron asconstantly gives at least eight per cent. by volume of ammonia under the conditions referred to, since iron can be produced accordin to our invention which gives smaller yiel than eight per cent., which may also diminish somewhat in use, but which is suflieiently active to enable the production of ammonia on a commercial scale to be carried out.

-B our invention we are therefore enabled to o tain ammonia in such quantities that a commercially successful production thereof can be carried out, and thus this most important compound can be produced while making use of free nitrogen obtained from the air.

\Ve have discovered that certain bodies when suitably mixed or compounded with iron impart to it the property of enabling the combination of nitrogen and hydrogen to take place to a higher degree than in the absence of such bodies. We have also further discovered that certain bodies appear to act as poi s on the catalytic property of iron, so that when such a body is present with the iron, any operty which it would above described, we mention arsenic, sulfur, is otherwise read for use as the catalytic selenium, tellurium, phosphorus, boron, an agent, or it can lie added to the materials timony, bismuth, lead, tin, and zinc and from which the catalytic agent is to be pretheir compounds. As a rule the elements pared. Naturally occurring iron oxid, or

hereinbefore mentioned exercise their deleiron hydroxid, which contains a suitable 7o terious efl'ect whether the said element be promoter according to this invention can added or be present as such or in the form be employed for the reduction of the cataof a suitable compound thereof. Carbon -lytic agent. Thus or instance, iron oxid monoxid and some other carbon compounds may be moistened with a solution contain- 10 are also poisonous. On the other hand, the ing caustic potash and then filled into the 75 catalytic power of iron to convert hydrogen reaction tube in which it is then reduced to and nitrogen into ammonia is enhanced by the metallic form by the hydrogen passing the presence of compounds of such elements over it, or iron may be mixe with, for as magnesium, beryllium, aluminium, the instance, magnesia, and the mixture may rare earth metals such as cerium,lanthanum; be dissolved in nitric acid, the solution obso erbium, neodymium praseodymium, samantained then being evaporated to dryness and um, yttrium, ytterlnum, and further pothe'mixture of nitrates calcined. On filling tassium, rubidium, caesium, sodium, lithium, the resulting mixture into the contact tube strontium, barium, calcium, uranium, thoriand passin through it the mixture of byum, zirconium, vanadium, niobium, tantadrogen an nitrogen, the iron oxid is re- ,lum, chromium, man anesc, mol bdenum. duced and a catalyt 0 agent is obtained and tungsten. These odies may termed which gives satisfactory yields of ammonia. promoters. For instance, mangesium Again, iron which is otherwise unsuitable may be added to the iron in the form of for use as a catalytic agent, either owing to 25 magnesium nitrate, and since itis evident its content of contact poison or for some 9 that during the passage of the mixture of other reason, can be rendered ellicient as a hydrogen and nitrogen over the contact macatalytic agent for the production of amterial, the body added may undergo some monia by heating it, either as such or, prefchemical change, we do not wish to be unerably, in admixture with a romoter, to a so derstood as confimng our invention to the high temperature, either in t e presence of 95 Q 85 terious e set, or on the other hand a very thereof and the resu use or otherwise of the specific compounds air or oxygen or other suitable compound, of the elements mentioned. The presence so that the iron and also the admixture, if v of very small quantities of the aforesaid such has been added, are converted, at an bodies ma be suflicient toexert a very delcrate for the greater 1part, into the oxi s ting product is re- 10o favorable efiect, on the catalytic ower of duced again with hydrogen free from conthe iron. For instance, such sm quantitact poison. The heat'm should preferties of the contact-poisons as occur someabl becarried outsothatghe mixture melts times in iron sold as pure or purest an may also be carried out in mono or in T40 may exert a very deleterious action, while on the presence of indifi'erent gases, provided 105 the other hand the presence of 0.2 per cent. that the conditions are such that a mixture of aluminium OX Id ma be suficient to inof oxids is obtained. The resulting mixture crease very considerab y the yield of am-. of oxid, after havin been broken up if moma obtained. To some extent the delenecessary, caneither he placed in the conterious action of a contact poison tact tube or furnace, or it can be previously 110 counteracted by the addition of a reduced, for instance with hydrogen. If which has the wer of promoting the catasuch treatment he applied to iron containing lytic action. us iron containing a small a contact poison, it appears to brin about proportign of sulfur has little or no catathe result that he iron is purifie thereytic action on a mixture of hydrogen and from, either by the said contact poisons 115 nitrogen, but if such iron containing a-small being entirely remo ed or converted into pro ortion of sulfur be suitably treated with an innocuous condition, and the iron is then ient magnesia, the poisonous action of capable of yielding satisfactory quantities the sulfur may be overcome, and the resultof ammonia. If one treatment does not 7 ing mixture may PM such a catalytic produce the desired result, it must be re- 12o ower that it may be employed in the manupeated. k k. acture of ammonia. The presence of a pro- Of course instead of employings'iron in motor in the iron is also of advantage in the. formof metal, those compoun thereofthose cases where without its presence, the such as oxide, hydroxide, nitride, and salts, power of the catalytic agent to produce amcan be emplo ed, ,which under the rondi- 12: monia diminishes as time goes on. V tions of wor 'ng are converted into the The body can be added to the iron in any metal. 7 suitable manner, for instance a metallic For the continued activity of the contact oxid, hydroxid, or salt or other suitable material, the gases should be free from compound, lee-added to the iron which bodies which act as contact poisons before 13' monoxid, or carbon dioxid, or

they are passed over the catalytic agent. In particular they should not contain carbon sulfur, or acompound thereof. They should also be free from oil.

It may be that our treatment of practically inert iron to convert it into the new form which can be used in the commerical manufacture of ammonia, removes, destroys,

or otherwise renders inert traces or small quantities of contact poisons in the iron, or it may introduce or render active traces or small uantities of promoters similarly presout, or oth these results may simultaneously occur. Or the result of the treatment may be a physical change, either alone or in addition to both or either of the above actions. We do not, however, bind ourselves to any theoretical explanation of the effect produced In the form preferred for carrying out the invention, we prefer to treat a very pure iron in the presence of a promoter and to use the iron so obtained in the presence of the said promoter in the manufacture of ammonia.

When our new form of iron is produced by the reduction of iron oxid, or other compound of iron, either with or without the addition of a promoter or the like, we prefer to reduce, the said oxid at as low a temperature as possible, since when our new form of iron which is capable of bringing about the combination of nitro n and hydrogen to the degree necessary drcommercial operations, is subjected to a high temerature, say eight hundred or nine hundred egrees centigrade, it tends to lose its catalytic power to a greater or lesser extent.

We prefer also, therefore, to employ as low a temperature as practicable for the production of ammonia, and it is a characteristic pro erty of our new form of iron that it enab es the production of ammonia to be carried out catalytically on a commercial scale at such a temperature that its catalytic action remains substantially constant.

The production of ammonia can be carried out under either ordinary or increased pressure.

Our new form of iron as hereinbefore described can, if desired, be employed for the purpose of producing ammonia when it is situated on a carrier, such for instance, as asbestos and chamotte. A carrier may be employed such that a constituent thereof constitutes a promoter in the sense hereinbefore defined, and this promoter may enter the iron and enhance its catal tic power. Or the iron may be brought nto the favorable form for the production of ammonia by a plying both the iron and the promoter, to t e carrier. If desired, these two methods of procedure may be combined. The followin examples will serve to illustrate further tn nature of our invention,

but we do not wish to be understood as restricting our invention in any way to these examples.

Example 1: Melt iron such as is sold as pure, but which contains traces of impuri- 7 ties, in a current of oxy en, so that molten iron oxid is formed. llowto cool and then break up the mass into small ieces and reduce it with. h drogen at as ow a temperature as possib e. t will be found to give a much better yield of ammonia than did the iron before such treatment. Repeat the treatment till no substantial further improvement results. The oxygen and hydrogen used must be free from contact poisons. Exam le 2: Take ordinary commercial iron oxid which is devoid of any catalytic action as regards the production of ammonia, mix it with five per cent. of potassium carbonate and treat the mixture in a monia. The oxygen and ydrogen used for the oxidation and reduction must be free from contact poisons.

Example 4: Moisten iron oxid with from three, to four, per cent. of its welght of caust1c potash dissolved in a small quantlty of water. Place the mixture in the contact tube or furnace and then reduce it with hydrogen free from contact poison.

In this example, instead of caustic otash, other hydroxid, salt, or other sultab e compound, can be employed, for instance, sodium carbonate, saltpeter, magnesium chlorid, or strontium nitrate.

Example 5: Mix iron with one-tenth of its weight of magnesia, dissolve the mlxture in pure nitric acid, eva orate the solut1on to dryness and convert t e nitrates into the 115 oxids by means of heat. Then reduce the mixture with hydrogen free from contact poison.

In this example, instead of magnesia. oxids and nitrates of alumimum, beryllium, or other rare earth, can be substituted.

Exam le 6: Dissolve together eciuahparts by weig t of iron nitrate and a umimum nitrate in water. Precipitate the hydI'OXIdS by means of pure ammonia and then filter, calcine, and reduce at as low a temperature as ossible the mixture of oxids obtained with hydrogen free from contact poison.

Example 7 Moisten iron oxid, which from its preparation already contains a suitable admixture,

such for instance as the Crocus mantis of commerce (Dammcr, H andbuch der chemischen Technolo z'e, vol. 4, p. 541), and press it into the orm of rods, place it in the contact tube or furnace and reduce it, either with hydrogen free from contact poison, or with ammonia, or with the mixture of hydrogen and nitrogen which is to be used for the manufacture of ammonia.

Example 8: Soak iron oxid in a solution of zirconium nitrate and then dry, and reduce the product in a current of hydrogen free from contact poison.

Example 9: Break magnetite, or hematite, free from arsenic and sulfur, into a coarse powder and reduce it with hydrogen free from contact poison. The product so obtained contains substances other than iron and produces much higher yields of ammonia when used as a catalytic agent than does a pure iron catalytic agent prepared from pure Fe o or Fe O Example 10: Mix together a solution of iron nitrate with ammonium molybdate, so that about equal parts by weight of iron and of molybdenum are employed; evaporate the mixture and heat it until the oxide are produced, and then reduce the mixture with hydrogen free from contact poison.

In this example, ammonium vanadate, or ammonium tungstate, can be substituted for the ammonium molybdate.

Example 11 Melt a pure iron with about two per cent. of pure aluminium oxid in a current of oxygen at a strong white heat. The product can be broken and employed as the catalytic agent afterhaving been reduced at as low a temperature as possible, either outside or inside the contact tube or furnace. The oxygen and hydrogen used must be free from contact poisons.

Example 12: Heat iron oxid with about three per cent. by weight of potassium carbonate to a temperature of one thousand degrees centigra e, and break into small pieces the mass obtained and reduce it with hydrogen free from contact poison.

Example 13: Mix iron with two per cent. by weig weight of lime, and one per of silica, then add two and weight the quantity of chlorate,- apply a light to t e mixture and break up the oxidized mass obtalned, and then reduce it with hydrogen free from contact poison.

Exam le 14: Soak purified asbestos with a solution containing iron nitrate and aluminium nitrate, then dry, .and reduce in a current of hydrogen hih .is free from contact poison.

Example 15: Heat porous grains of clay for some. time with a solution of iron mtrate, dry the whole, and then fill it into cent. by weight a half times by potassium perhundred degrees centigra combining pro t of magneisum, two per cent. by

the contact tube. Then reduce in a current of hydro n free from contact poison. If desired, t e reduction may be carried out before the mixture is introduced into the contact tube. The constituents of the clay which have gone into solution help to increase the catalytic activity of the iron.

Instead of clay, another carrier which behaves in a similar manner may be employed.

Example 16: In order to obtain ammonia, pass a current of gas containing three volumes of hydrogen and one volume of nitrogen through a contact tube containing a contact material which has been prepared according to the foregoing example 11, while maintaining a temperature of between four hundred and fifty and five hundred and fifty degrees centigrade, and at a pressure of two hundred atmospheres.

Example 17: iMelt a pure iron with five per cent. of pure aluminium in a current of pure oxygen and reduce the iron oxid by means of pure hydrczigen. Then ass a current of nitrogen an hydrogen in combinmg proportions over the resulting mixture at a tem erature of from four hundred to five hun red degrees centigrade at atmospheric pressure.

Exam le 18: Place as pure an iron oxid as possible in a contact tube and pass a current of pure hydrogen and nitrogen through it while maintaining a temserature below six e, and then, when the end is reduced, continue passing the mixture of pure hydrogen and nitrogen in ortions, never allowing the temperature 0 the contact mass to rise above six hundred degrees centigrade, and maintaining a pressure of one hundred and fifty atmospheres.

We do not claim in this present application generically the production of ammonia while making use of a. catalytic agent together with a promoter in each case, such production and such catalytic mixtures bemg embodied in the claims of Patent No. 1,094,194, neither do we claim in this ap lication the production of makin use of the catalysts of the present invention, since such manufacture of ammonia is claimed in our divisional application Serial No. 869,147 filed Oct. 28, 1914.

Now what we claim is 1. A new form of iron which is an active catalytic agentfor the manufacture of ammonia from its elements.

2. A new form catalytic agent for the monia from its elements and retains its catalytic power while in use in the absence of contact poison so as to applicable to the manufacture of ammoma from its elements for several w manufacture of amammonia w e of iron which is an active 3. An active catalyst for the manufacture iron and a promoter substantially as described.

4. An active catalyst for the manufacture of ammonia from its elements consisting of iron and aluminium oxid.

5. An active catalyst for the manufacture of ammonia from its elements consisting of ninety-eight per cent. of iron and two per cent. of aluminium oxid.

6. The process for the manufacture of a new form of iron which is an active catalyst for the manufacture of ammonia from its elements, by oxidizing iron in the presence of oxygen ree from contact poisons and reducing the iron oxid obtained with hydrogen free from contact poisons and repeating the treatment if necessar 7. The process of manufacturing an active catalyst for the manufacture of ammonia from its elements, consisting in heating a mixture of iron and a promoter in a current of oxygen free from contact poison and then treating the product with hydrogen free from contact poison substantially as de scribed.

In testimony whereof we have hereunto set our hands inthe presence of two subscribing witnesses.

CARL BOSCH. ALWIN MITTASCH. HANS WOLF. GEORG STERN.

Witnesses:

ERNST F. EHRHARDT, J. ALEx. LLOYD.

It is hereby certified that in Letters Patent No. 1,148,570, granted August 3,

1915, upon the application of Carl Bosch, Alwin Mjttasch, and Hans Wolf, of LudWigshafemon-the-Rhine, and Georg Stern, of Mannheim, Germany, for an improvement in Catalytic Agents for Use in Producing Ammonia, errors appear in the printed specification requiring correction as follows: Page 2, line 23, for the word mangesium reed magnesium; page 4, line 50, for the word magneisum read magnesium; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 2nd day of November, A. D., 1915.

R F. WHITEHEAD,

Acting Commissimwr of Patents. 

